SN Certified Technician

There is a 1" x 1.5" plastic sticker on the end of the computer opposite the wiring connector.

Computer & interchange information for 5.0 Mustang

Revised 16-Oct-2011 to add O2 sensor harness warnings

The Mass Air computers from 89-93 are interchangeable with a few exceptions. Just be sure you use the MAF & MAF sensor from the same series computer. The auto transmission computers use a different start circuit than the manual computers. You can use an auto trans computer in a 5 speed car with no problems or changes. I have done it in my original 89 Mustang GT, and I know it works OK. I would recommend avoiding using a 5 speed computer in an auto trans car due to the possibility of damaging the computer’ internal signal ground circuitry.

The odd duck is the 93 Cobra computer, labeled X3Z which is internally calibrated for 24 lb injectors. Use the MAF & MAF sensor from the X3Z computer to avoid problems with the computer's internal calibration. Try and avoid the 93 Cobra computer if you can.

Some cautions about O2 Sensor harnesses need to be observed to avoid damage to the computer.
Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans will cause no crank problems.
See http://forums.corral.net/forums/general-mustang-tech/1094179-oxygen-sensor- harnesses-manual-auto-differences-year-differences.html for more O2 sensor wiring harness info
If you have a damaged computer with signal ground problems, See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.

I kinda have a Frankenstein. My mustang is an 85 with what is supposed to be an 88 motor. The EEC is the VM1 which is correct for the car year. The VM1 is a speed density EEC but if I'm not mistaken it should be for a carbureted engine. Will the EEC work correctly with the 88 SD FI engine? I'm trying to chase down some gremlins.

Thank you for the reply. So the EEC is correct for the year of the car but one of the owners before me swapped in an 88 H.O. 5.0 EFI engine. Will the VM1 EEC work with the later engine or should I start hunting for the correct EEC?

SN Certified Technician

It should work OK. If you aren't having other problems your current computer should do the job.

To find any other problems that he computer has detected, dump the codes.
Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. I highly suggest that you read it and follow the instructions to dump the codes.

It should work OK. If you aren't having other problems your current computer should do the job.

To find any other problems that he computer has detected, dump the codes.
Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. I highly suggest that you read it and follow the instructions to dump the codes.

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Thank you. I've gotten a KOEO code of 67, had to bypass it as you stated for the KOER by grounding pin 30 and then have gotten codes 21, 44, and 94. I know what those codes are and will be trying to remedy them. The biggest gremlin I've got is the car failed an emissions test with very high HC, but NOx and CO were within tolerance. A friend thought that it might be a vacuum leak but if it is it's small as the car has 15" vacuum at idle.